This invention relates to optical magnifying devices and more particularly to an optical magnifying device having several modes of positional adjustability and adapted for use as an attachment to a grooved triangular ruler or scale.
Triangular rulers or scales, as used by architects, engineers and draftsmen in preparing precision drawings or in making accurate measurements from existing drawings, contain several different linear scales, the subdivisional markings of which may be difficult to discern with the unaided eye. The use of magnifying glasses of various types have been earlier disclosed to render the markings of the ruler more legible. There has further been disclosed the use of magnifying glasses associated with mechanical structure permitting the magnifying glass device to slideably engage the longitudinal grooves generally present in each side of said triangular rulers. Such devices, as may be found for example in U.S. Pat. Nos. 1,806,422; 1,773,899 and 2,502,039, although improving the ease of reading the markings, lack the versatility of positional adjustment needed by those who use said rulers.
The need for adjustability of the magnifying glass is dictated by the fact that, to derive the sought benefit, the marking, the center of the magnifying glass, and the user's eye should be on substantially the same straight line or optical axis. This is not always readily accomplished under ordinary circumstances because the ruler may be used on an inclined or horizontal surface or may be positioned at different distances from the user's eyes, or may be oriented in different directions on the surface upon which the work is being done. Although the magnifying glass of U.S. Pat. No. 1,806,422 appears to have a lateral mode of positional adjustability, unless said magnifying glass is positioned directly above the ruler to which it is attached, it will cause the combined ruler-magnifying glass assembly to tip over, especially on an inclined surface. Obvious expedients which might be resorted to in order to secure the ruler to the work surface for improved postural stability would interfere with the necessary mobility of the ruler.
It is accordingly an object of the present invention to provide an optical magnifying device adapted for slideable attachment to a grooved triangular ruler.
It is another object of this invention to provide a device of the aforementioned nature having several modes of positional adjustment.
It is a further object to provide a device of the aforementioned nature having improved postural stability without interfering with the mobility of the ruler.
These objects and other objects and advantages of the invention will be apparent from the following description.